Wire cords comprising at least three wire filaments arranged about a continuous core filament are known, they serving, more particularly, for reinforcing pneumatic tires such as, for example, car and truck tires. Such wire cord inserts in tires are known as belted cord inserts.
When employed in van and truck tires such wire cord inserts or strengthenings are subjected to higher stresses than when used in car tires, this being the reason why the demands on wire cords reinforcing truck tires being higher. Accordingly, when cheap-production steel cords having a simple configuration, as employed for example in car tires, are used in van and truck tires belt edge detachment may easily occur.
Such simply configured steel cords consist, for example, of a core composed of three wire filaments having a diameter of 0.2 mm as well as six 0.35 mm diameter wire filaments arranged about this core. Producing such a steel cord is simple and in general presents no problem in processing. As already mentioned, however, due to its stiffness, detachment of the belt edge may easily occur in the tire, making the tire useless.
This risk of the belt edge becoming detached is significantly diminished in the case of cords produced at more expense having a higher number of wires (for example steel cords having a core cord of three wire filaments wrapped by nine wire filaments and a sheathing ply of a further fifteen wire filaments each having a diameter of 0.22 mm as well as a spiral wire of 0.15 mm diameter surrounding this structure). However, due to the geometric assignment of the individual wires relative to each other inner cavities automatically materialize in the case of such wire cords having a higher wire number, it then no longer being possible for the embedding rubber to penetrate therein so that the adhesive bond of the embedding rubber remains limited to the outer casing sections. On top of this, moisture contained in the entrapped air has a corrosive effect on the wire cords from within and contributes towards the wires becoming prematurely aged and ruined.
Known from DE 26 48 524 A1 is a wire cord as a medium for strengthening rubber items which is configured of three or more solid metal wires twisted together about a continuous core of a non-metallic compressible material. More particularly this non-metallic compressible material is a vulcanizable rubber, a thermoplastic, an aromatic polyamide or a natural or man-made fiber material. By employing such a non-metallic compressible material as the core of a wire cord the vacant space otherwise existing in the wire cord is practically or substantially filled out, as a result of which displacements of individual outer wires under the influence of lateral compressive forces are avoided. Filling out the vacant spaces in the wire cord in this way is achieved by the elastomer or textile core yielding to the steel wires grouped about the core when the steel cord is processed in the tire so that the steel wires are able to approximate each other and slightly deform the core wire.
Known from DE-PS 816 308 is a reinforcing insert for items made of rubber, the wire cords of which comprise a non-vulcanized or prevulcanized rubber core in which the individual wires are located spaced away from each other. Due to these rubber cores the cords are endowed with a high elastic strain so that the wire cord features higher flexibility.
Known from DE-OS 2 209 752 are wire cords as reinforcing inserts in conveyor belts consisting, for example, of wire filaments arranged about an elastomer core.